Methods and systems for determining fluid content of tissue

ABSTRACT

Diagnostic apparatus includes a plurality of antennas, which are configured to be disposed at different, respective locations on a thorax of a living body so as to direct radio frequency (RF) electromagnetic waves from different, respective directions toward a heart in the body and to output RF signals responsively to the waves that are scattered from the heart. Processing circuitry is configured to process the RF signals over time so as to provide a multi-dimensional measurement of a movement of the heart.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of PCT patent applicationPCT/IB2009/055438, filed Dec. 1, 2009, whose disclosure is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to methods and systems formedical diagnostic measurement and monitoring, and specifically to radiofrequency (RF)-based measurement and monitoring of the heart.

BACKGROUND OF THE INVENTION

RF imaging is best known in the context of radar systems, but RFdiagnostic imaging and measurement systems have also been developed formedical applications. For example, U.S. Patent Application Publication2008/0169961, whose disclosure is incorporated herein by reference,describes computerized tomography using radar, which may be used forgenerating an image of living tissue.

As another example, U.S. Patent Application Publication 2009/0299175,whose disclosure is incorporated herein by reference, describes a methodand apparatus for determining and tracking the location of a metallicobject in a living body, using a radar detector adapted to operate on aliving body. Applications described in this publication includedetermination of the extent of in-stent restenosis, performingtherapeutic thrombolysis, and determining operational features of ametallic implant.

Yet another example is U.S. Pat. No. 5,766,208, whose disclosure isincorporated herein by reference. This patent describes a non-acousticpulse-echo radar monitor, which is employed in the repetitive mode,whereby a large number of reflected pulses are averaged to produce avoltage that modulates an audio oscillator to produce a tone thatcorresponds to the heart motion. The monitor output potential can beseparated into a cardiac output indicative of the physical movement ofthe heart, and a pulmonary output indicative of the physical movement ofthe lung.

U.S. Pat. No. 4,926,868, whose disclosure is incorporated herein byreference, describes a method and apparatus for cardiac hemodynamicmonitoring based on the complex field amplitudes of microwavespropagated through and scattered by thoracic cardiovascular structures,particularly the heart chambers, as a function of time during thecardiac cycle. The apparatus uses conformal microstrip antennas thatoperate in the UHF band. The basic measurement technique is vectornetwork analysis of the power wave scattering parameter.

U.S. Patent Application Publication 2009/0240133, whose disclosure isincorporated herein by reference, describes a radio apparatus and methodfor non-invasive, thoracic radio interrogation of a subject for thecollection of hemodynamic, respiratory and/or other cardiopulmonaryrelated data. A radio transmitter transmits an unmodulated radiointerrogation signal from an antenna into a subject, and a radioreceiver captures, through the antenna, reflections of the transmittedradio interrogation signal returned from the subject. A Dopplercomponent of the reflections contains the data that can be extractedfrom the captured reflections.

SUMMARY OF THE INVENTION

Embodiments of the present invention that are described hereinbelowprovide methods and devices for assessment of cardiovascular function bytransmission and detection of RF waves through the body.

There is therefore provided, in accordance with an embodiment of thepresent invention, diagnostic apparatus, including a plurality ofantennas, which are configured to be disposed at different, respectivelocations on a thorax of a living body so as to direct radio frequency(RF) electromagnetic waves from different, respective directions towarda heart in the body and to output RF signals responsively to the wavesthat are scattered from the heart. Processing circuitry is configured toprocess the RF signals over time so as to provide a multi-dimensionalmeasurement of a movement of the heart.

In some embodiments, the plurality of antennas includes at least threeantennas, and the respective locations are chosen so as to at leastpartially surround the thorax.

In disclosed embodiments, each antenna has a front surface, which isconfigured to contact an outer surface of the body and includes a planarantenna element. The planar antenna element may include a conductivespiral. Additionally or alternatively, each antenna may include a groundplane behind the front surface with an electromagnetic band gap (EBG)structure between the ground plane and the front surface. Typically, adielectric gel is applied between the antenna and the outer surface ofthe body.

In one embodiment, each antenna is configured to contact an outersurface of the body and, the processing circuitry is configured toreceive and process an electrocardiogram signal received from the bodyby at least one of the antennas, in addition to the RF signals.

In a disclosed embodiment, the apparatus includes excitation circuitry,which is coupled to select different ones of the antennas to serve astransmitting and receiving antennas and to apply a RF excitationwaveform at multiple different frequencies to the selected transmittingantennas, while the processing circuitry receives the RF signals fromthe selected receiving antennas, wherein the transmitting and receivingantennas and the different frequencies are selected according to apredetermined temporal pattern. Typically, the excitation circuitryincludes a driver circuit, which is configured to generate the RFexcitation waveform with a variable frequency, and a switching matrix,which is configured to select sets of the antennas in alternation, eachset including at least one transmitting antenna and at least onereceiving antenna, and for each selected set, to couple the drivercircuit to excite the at least one transmitting antenna at a selectedfrequency while coupling the processing circuitry to receive the RFsignals from the at least one receiving antenna.

In one embodiment, the plurality of antennas includes at least first andsecond antennas disposed on respective opposite sides of the thorax, sothat the second antenna receives the RF electromagnetic wavestransmitted by the first antenna after passage of the RF electromagneticwaves through at least one lung in the body, and the processor isconfigured to process the RF signals output by the second antenna so asto assess an amount of fluid accumulation in the at least one lung.

In another embodiment, the apparatus includes at least one pacingelectrode, wherein the processing circuitry is configured to drive theat least one pacing electrode so as to pace the heart responsively tothe measurement of the movement of the heart.

In yet another embodiment, the processing circuitry is configured tocompare the measure of the movement of the heart before, during andafter heart stress.

There is also provided, in accordance with an embodiment of the presentinvention, diagnostic apparatus, including an antenna, which isconfigured to be disposed on a thorax of a living body so as to directradio frequency (RF) electromagnetic waves toward a heart in the bodywhile sweeping the waves over multiple different frequencies and tooutput an ultra-wideband RF signal responsively to the waves that arescattered from the heart. Processing circuitry is configured to processthe RF signal over time so as to provide a measurement of a movement ofthe heart.

In some embodiments, the apparatus includes a package, which containsthe antenna and the processing circuitry and is configured to be affixedas a patch to an outer surface of the body. The apparatus may include aconductive element associated with the package, which is configured toreceive electrocardiogram (ECG) signals from the outer surface of thebody. Additionally or alternatively, the apparatus includes a wirelesscommunication interface for communicating with a remote console.

There is additionally provided, in accordance with an embodiment of thepresent invention, diagnostic apparatus, including one or more antennas,which are configured to be disposed on a thorax of a living body so asto direct radio frequency (RF) electromagnetic waves through a lung inthe body and to output RF signals responsively to the waves that havepassed through the lung. Processing circuitry is configured to processthe RF signals over time so as to measure RF path characteristic of theRF electromagnetic waves and, based on the path characteristic, toassess a fluid content of the lung.

The processing circuitry may be configured to measure a change in thepath characteristic over one or more respiratory cycles of the lung, andto assess the fluid content responsively to the change.

In disclosed embodiments, the path characteristic includes an effectiveRF path length of the RF electromagnetic waves through the body. In someembodiments, the processing circuitry is configured to receive a measureof a physical distance traversed by the RF electromagnetic waves throughthe thorax, and to compare the effective RF path length to the physicaldistance in order to assess the amount of the fluid accumulation. In oneembodiment, the one or more antennas include a transmitting antenna at afirst location on a first side of the thorax, which transmits the RFelectromagnetic waves through the lung, and a receiving antenna, whichreceives the waves that have passed through the lung at a secondlocation on a second side of the thorax, opposite the first side, andthe physical distance is measured between the first and secondlocations.

Alternatively, the one or more antennas include at least one antennathat is configured to direct the RF electromagnetic waves through thelung toward a heart in the body, and to output the RF signalsresponsively to the RF electromagnetic waves reflected from the heart.The apparatus may include an ultrasonic transducer, which is adjacent tothe at least one antenna and is configured to direct ultrasonic wavestoward the heart and receive the ultrasonic waves reflected from theheart so as to provide a measure of the physical distance.

Additionally or alternatively, the path characteristic includes anamplitude of the RF signals.

There is further provided, in accordance with an embodiment of thepresent invention, diagnostic apparatus, including an antenna unit,which has a front surface configured to be brought into contact with anouter surface of a living body. The antenna unit includes a planarantenna element, which is configured to direct radio frequency (RF)electromagnetic waves from the front surface into the body and to outputRF signals responsively to the waves that are scattered from within thebody, and a conductive element, which is configured to receiveelectrocardiogram (ECG) signals from the outer surface of the body. Acable is connected to the antenna unit so as to communicate with theplanar antenna element and the conductive element. Processing circuitryis connected to the cable so as to receive and process the RF and ECGsignals.

Typically, the apparatus includes a diplexer coupled between the cableand the processing circuitry for separating the RF signals from the ECGsignals.

The antenna unit may include an adhesive patch for attachment to thebody. Alternatively, the antenna unit may be configured to be worn onthe body as part of a garment.

In a disclosed embodiment, the antenna unit is coated with metal andelectrolytes.

There is moreover provided, in accordance with an embodiment of thepresent invention, diagnostic apparatus, including an antenna unit,which has a front surface configured to be brought into contact with anouter surface of a living body. The antenna unit includes a planarantenna element, which is formed on the front surface and is configuredto direct radio frequency (RF) electromagnetic waves into the body andto output RF signals responsively to the waves that are scattered fromwithin the body, with a ground plane behind the front surface and anelectromagnetic band gap (EBG) structure between the ground plane andthe front surface. Processing circuitry is coupled to the antenna unitso as to receive and process the RF signals.

There is furthermore provided, in accordance with an embodiment of thepresent invention, therapeutic apparatus, including at least one pacingelectrode, configured to apply a pacing signal to a heart in a livingbody. One or more antennas are configured to be disposed on a thorax ofthe body so as to direct radio frequency (RF) electromagnetic wavestoward the heart and to output RF signals responsively to the waves thatare scattered from the heart. Processing circuitry is configured toprocess the RF signals over time so as to measure a movement of theheart and to drive the at least one pacing electrode so as to pace theheart responsively to the measured movement.

There is also provided, in accordance with an embodiment of the presentinvention, a method for diagnosis, including directing radio frequency(RF) electromagnetic waves from a plurality of antennas, which aredisposed at different, respective locations on a thorax of a livingbody, toward a heart in the body from different, respective directions,and outputting RF signals responsively to the waves that are scatteredfrom the heart. The RF signals are processed over time so as to providea multi-dimensional measurement of a movement of the heart.

There is additionally provided, in accordance with an embodiment of thepresent invention, a method for diagnosis, including directing radiofrequency (RF) electromagnetic waves from an antenna, which is disposedon a thorax of a living body, toward a heart in the body while sweepingthe waves over multiple different frequencies, and outputting anultra-wideband RF signal responsively to the waves that are scatteredfrom the heart. The RF signal is processed over time so as to provide ameasurement of a movement of the heart.

There is further provided, in accordance with an embodiment of thepresent invention, a method for diagnosis, including directing radiofrequency (RF) electromagnetic waves from one or more antennas disposedon a thorax of a living body so that the waves pass through a lung inthe body, and outputting RF signals responsively to the waves that havepassed through the lung. The RF signals are processed over time so as tomeasure a RF path characteristic of the RF electromagnetic waves and,based on the path characteristic, to assess a fluid content of the lung.

There is moreover provided, in accordance with an embodiment of thepresent invention, a method for diagnosis, including bringing a frontsurface of an antenna unit into contact with an outer surface of aliving body. The antenna unit included a planar antenna element and aconductive element, which is configured to receive electrocardiogram(ECG) signals from the outer surface of the body. The planar antennaelement is driven to direct radio frequency (RF) electromagnetic wavesfrom the front surface into the body and to output RF signalsresponsively to the waves that are scattered from within the body. Boththe RF and the ECG signals from the antenna unit are received andprocessed.

There is furthermore provided, in accordance with an embodiment of thepresent invention, a therapeutic method, including directing radiofrequency (RF) electromagnetic waves toward a heart in a living bodyfrom one or more antennas disposed on a thorax of the body, andoutputting RF signals responsively to the waves that are scattered fromthe heart. The RF signals are processed over time so as to measure amovement of the heart, and the heart is paced responsively to themeasured movement.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration showing a system formonitoring of heart function, in accordance with an embodiment of thepresent invention;

FIG. 2 is a schematic representation of a display screen in a system formonitoring of heart function, in accordance with an embodiment of thepresent invention;

FIG. 3 is a block diagram that schematically shows functional elementsof a system for monitoring of heart function, in accordance with anembodiment of the present invention;

FIG. 4 is a schematic exploded view of a patch antenna, in accordancewith an embodiment of the present invention;

FIGS. 5A and 5B are schematic plots of propagation delay and amplitude,respectively, of RF waves reflected from the heart, in accordance withan embodiment of the present invention;

FIG. 6 is a schematic, pictorial illustration showing elements of asystem for diagnosis of pulmonary edema, in accordance with anembodiment of the present invention;

FIG. 7 is a schematic, pictorial illustration showing elements of asystem for pacing the heart, in accordance with an embodiment of thepresent invention; and

FIG. 8 is a block diagram that schematically illustrates a patch antennaunit, in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

PCT Patent Application PCT/IB2009/055438, whose disclosure isincorporated herein by reference, describes the use of radar imagingtechniques to identify and locate features in the body, based on thedifference in their complex dielectric constant relative to thedielectric constant of the surrounding tissue. In the disclosedembodiments, an array of antennas (also referred to as antenna elements)directs RF electromagnetic waves toward the heart and receives the wavesthat are scattered from within the body. Excitation circuitry applies aRF excitation waveform at multiple different frequencies to differenttransmitting antennas in the array. Processing circuitry receives andprocesses signals from different receiving antenna elements in order tolocate a feature or features of interest, and possibly to track themovement of such features over the course of the heart cycle. Theselection of transmitting and receiving antennas, as well as theselection of excitation frequency, follows a predetermined temporalpattern, which may be implemented by a switching matrix connected to theantenna elements.

As a result of this scheme of excitation and reception, the processingcircuitry receives and processes signals from multiple spatial channels(corresponding to different pairs of antennas) at multiple differentfrequencies for each channel. Taken together in the time domain, thesemulti-frequency signals are equivalent to short pulses of RF energy. Toreconstruct a three-dimensional (3D) image of the interior of the bodyand find the location of a feature or features, the processing circuitryapplies a spatial transform to the set of received signals. Thetransform may, for example, comprise an inverse spherical Radontransform or an algebraic approximation of such a transform.

Embodiments of the present invention that are described hereinbelowapply techniques similar to those described in PCT/IB2009/055438 forpurposes of cardiovascular diagnosis and therapy. In one embodiment,multiple antennas are disposed at different, respective locations on thethorax of a patient, typically surrounding all or at least a part of thethorax. The antennas direct RF waves from different, respectivedirections toward the heart and output RF signals in response to thescattered waves that they receive. The RF signals received over time areprocessed so as to provide a multi-dimensional (two- or eventhree-dimensional) measurement of movement of the heart. This approachcan give a picture of heart wall movement that resembles the sort ofinformation provided by cardiac ultrasound imaging, but does not requirethe active involvement of an expert operator and can even be carried outover a long period while the patient is ambulatory.

Heart wall motion measured by embodiments of the present inventionprovides detailed diagnostic information regarding functioning of theheart muscle. For example, the heart motion information is useful indiagnosis and monitoring of cardiac ischemia and heart failures, and canalso give an indication of cardiac performance, such as chamber volumeor ejection fraction. The information provided by embodiments of thepresent invention can be used in diagnosis, as well as prediction, ofischemic disease and/or ischemic events, such as acute myocardialinfarction. The heart wall motion may be compared before, during andafter heart stress caused by physical exercise or by medication, in amanner similar to ECG-based stress testing.

As yet another example, the heart wall motion information provided byembodiments of the present invention may be used in place of ultrasonicimaging data in analyzing and diagnosing cardiac mechanical function.For instance, radar-based measurements may be used instead of theDoppler imaging techniques described by Larsson et al., in “StateDiagrams of the Heart—a New Approach to Describing Cardiac Mechanics,”Cardiovascular Ultrasound 7:22 (2009), which is incorporated herein byreference.

Additionally or alternatively, embodiments of the present invention canbe used in long-term monitoring of heart conditions, and particularly asan ambulatory monitor for the detection of “silent ischemias” incoronary artery disease. Heart wall motion monitoring of this sort canthus be used as a diagnostic tool in addition to or instead ofconventional stress testing or Holter monitoring.

The heart motion information provided by embodiments of the presentinvention may also be used for therapeutic purposes. For example, in oneembodiment, a pacemaker is driven to pace the heart based on this sortof measurement, as an addition to other parameters, so that theamplitude and timing of the pacing signal give an optimal result interms of the actual profile of contraction of the heart muscle. Thissort of approach can be particularly useful in cardiac resynchronizationtherapy.

In some embodiments, these RF-based techniques are used to assess fluidaccumulation in the lungs, typically for diagnosis and follow-up ofpulmonary edema or lung congestion. In these embodiments, one or moreantennas on the thorax direct RF waves through one (or both) of thelungs and output RF signals in response to the waves that have passedthrough the lung. The RF signals are processed over time in order tomeasure a path characteristic of the RF waves passing through the body,such as the effective RF path length of the RF waves. The RF pathlength, as opposed to the actual, physical distance, is defined by thelength of time required for the waves to pass through the chest (eitherdirectly, from one side to the other, or by reflection from the heartand return to an antenna). This path length depends on the dielectricconstant of the tissue along the path. When there is fluid in the lungs,the dielectric constant is greater (relative to normal, air-filledlungs), and the RF path length increases accordingly. This RF pathlength may thus be used to assess the fluid content of the lung.

In some embodiments, monitoring information is sent from a localcontroller attached to the antennas on the patient's body to a centerwhere is the information can be accessed by a referring physician,experts, technicians, and/or the patient himself. The data may flow viaa local gateway device, such as a cell-phone or personal computer, via anetwork, such as the Internet or telephone network, to the center, whereit is stored.

Various types of antennas may be used in implementing embodiments of thepresent invention, including the sort of cavity-backed antenna that isdescribed in PCT/IB2009/055438. Alternatively, some embodiments of thepresent invention use a planar antenna comprising a conductive spiral,which is formed on the front surface of the antenna. The antenna isbacked by an in-phase reflective structure based on an electromagneticband gap (EBG) structure between the antenna ground plane and the frontsurface. This design provides a flat, possibly flexible antenna, whichcan be fixed to the body surface by a gel or other adhesive. (Suitabletypes of gels for this purpose are described in PCT/IB2009/055438.) Theantenna may also comprise a conductive element, which receiveselectrocardiogram (ECG) signals from the body surface along with the RFsignals output by the antenna itself. The antenna thus performs twocomplementary measurements simultaneously and obviates the need forseparate ECG electrodes.

In one embodiment, the antenna is part of a self-contained patch thatalso includes radar processing circuits and a power source. The patchmay also include a transmitter, such as a wireless unit, fortransmission of data to a monitor or gateway.

System Description

FIG. 1 is a schematic, pictorial illustration of a system 20 formonitoring the function of a heart 22, in accordance with an embodimentof the present invention. Multiple antennas 24, 26, 28, 30, 32 aredisposed at different, respective locations around a thorax 34 of thepatient. (The thorax is transparent in the figure so as to make visibleheart 22 and lungs 36, as well as antennas 28 and 30 on the patient'sside and back.) The antennas in this embodiment partially surround thethorax. In alternative embodiments, a larger number of antennas maysurround the thorax completely. In other embodiments, a smaller numberof antennas, possibly only one or two antennas, may be used. The use ofthree or more antennas, however, is advantageous in providingmulti-dimensional heart motion data, as explained further hereinbelow.

Typically, for good RF coupling, antennas 24, 26, 28, 30, 32 are fixedto the skin of the torso. For this purpose, the antennas may have theform of adhesive patches, as described in greater detail with referenceto FIG. 4, for example. Additionally or alternatively, for improvedcoupling, a dielectric gel may be spread between the front surfaces ofthe antennas and the skin, as described, for example, in theabove-mentioned PCT/IB2009/055438. This gel may have a high dielectricconstant at microwave frequencies, to give good RF impedance matching,and high conductivity at low frequencies to enhance electrocardiogramsignal acquisition. Further additionally or alternatively, the antennasmay be attached to and held in place by a suitable garment, such as avest (not shown), which the patient wears during the monitoringprocedure. Typically, the procedure takes a short time, on the order ofa few hours or less, although it is possible to monitor patients in thismanner over the course of a day or even several days.

Antennas 24, 26, 28, 30, 32 are connected by cables 38 to a controlconsole 40. The console comprises a front end 42, which drives theantennas to direct RF electromagnetic waves from different, respectivedirections toward heart 22. In response to the waves that are scatteredfrom the heart (and from other features in the body), the antennasoutput RF signals. Front end 42 receives these signals via cables 38,filters and digitizes the signals, and passes the resulting digitalsamples to processing circuitry 44. This processing circuitry processesthe RF signals over time so as to provide a multi-dimensionalmeasurement of movement of the heart, as shown and described below.Typically, processing circuitry 44 comprises a general-purpose computerprocessor, which is programmed in software to carry out the functionsdescribed herein. Additionally or alternatively, processing circuitry 44may comprise dedicated or programmable hardware logic circuits.

In the pictured embodiment, processing circuitry 44 drives a display 46to show a measurement of the movement of the heart, either graphicallyor numerically, or both. Additionally or alternatively, the processingcircuitry may make other measurements based on the RF signals, such asmeasuring the amount of fluid accumulated in lungs 36, as described ingreater detail hereinbelow. Further additionally or alternatively, frontend 42 may receive ECG signals from the antennas on the body surface,and processor 44 may process and output ECG information in addition tomeasurement of heart motion. The combination of ECG and motionmeasurement in a single unit is efficient and useful in providing acomplete picture of heart function, both electrical and mechanical.

In some embodiments, it is useful to know the precise locations, andpossibly also the orientations, of the antennas. For this purpose,antennas 24 and 30 are shown in the figure as comprising positionsensors 48. (The other antennas may also comprise position sensors, butthese sensors are omitted from the figures for the sake of simplicity.)Various types of position sensors that are known in the art, such asmagnetic, ultrasonic, optical or even mechanical position sensors, maybe used for this purpose. PCT/IB2009/055438 includes further details ofsuch position sensors and their integration in a radar-based measurementsystem.

FIG. 2 is a schematic representation of the screen of display 46 insystem 20, in accordance with an embodiment of the present invention.Typically, the display is configurable by the user to show differentmeasurements in various different formats. In the example shown in FIG.2, display 46 shows traces 50 that are indicative of the motion ofselected points on the heart wall over time, as measured by system 20.An ECG trace 52 is displayed alongside the wall motion traces forcomparison. (Although only two motion traces and one ECG trace are shownin FIG. 2 for the sake of simplicity, a larger number of traces mayalternatively be displayed.)

A graphical window 54 gives a two-dimensional (2D) view of the measuredheart motion and also enables the user to choose the points whose motionis to be shown by traces 50. Alternatively, given a sufficient number ofmeasurement points around the heart, window 54 may show a real-timethree-dimensional (3D) representation of heart wall motion.

Display 46 may optionally include other information and user interfacefeatures. For example, a parameter window 56 may show parameters derivedfrom the measurements made by system 20, such as cardiovascular and/orrespiratory parameters, in either graphical or numerical form (or both).A status window 58 shows the current status of each of the antennas.This window may indicate, for example, an antenna that is not properlyattached to the body (based on measurement of impedance between theantenna and the skin or on characteristics of the RF signals from theantenna), so that the operator can correct the situation. A controlwindow 60 displays status messages and operational buttons to turnsystem functions on and off.

FIG. 3 is a block diagram that schematically shows functional elementsof system 20, and specifically of front end 42, in accordance with anembodiment of the present invention. The elements of the front endexchange data and control instructions via a high-speed bus 62, which isconnected to processing circuitry 44 via a bridge 64. To enable ECGmeasurements, antennas 24, 26, 28, 30, 32 are connected via cables 38and a switching matrix 78 to a diplexer 66 at the input to front end 42.The diplexer separates out the low-frequency ECG signals from the RFsignals, passing the ECG signals to an ECG preprocessing circuit 68.This circuit filters and digitizes the ECG signals and passes the ECGdata via bus 62 to processing circuitry 44.

Front end 42 comprises a RF generator 70, which serves as a drivercircuit to generate signals at multiple different frequencies forexciting the transmitting antennas. A RF digitizer 72 demodulates anddigitizes the signals received by the receiving antennas. Typically, thesignals are in the range of about 400 MHz to about 4 GHz, althoughhigher and lower frequencies outside this range may also be used. An I/Qcancellation unit 74 performs signal conditioning functions, includingamplification of the outgoing and the incoming signals and cancellationof background components in the received signals. The backgroundcancellation functions of unit 74 are controlled by an I/Q controller76, as is described in greater detail hereinbelow.

Switching matrix 78 selects different sets of the antennas to transmitand receive signals at different, respective times and frequencies, in apredetermined temporal pattern. Typically, the sets comprise pairs ofantennas—one transmitting and one receiving. Alternatively, theswitching matrix may select a set consisting of a single monostaticantenna, which both transmits and receives. Further alternatively, otherantenna groupings may also be used. The structure and operation of aswitching matrix of this sort are described in detail inPCT/IB2009/055438. Switching matrix 78 and RF generator 70 togetherserve as excitation circuitry and generate a temporal excitation patterncomprising a sequence of measurement frames, wherein each frametypically defines a sweep of the excitation signal both in frequency andover spatial channels (antennas or antenna pairs). The beginning of eachframe is triggered by a trigger controller 80, which also provides aclock input to the other components of front end 42.

The sweep over multiple different frequencies creates, in effect, anultra-wideband signal, which is equivalent, in the signal processingdomain, to a very short radar pulse. The use of this sort ofultra-wideband signal enables system 20 to measure path length and heartwall range more accurately and robustly than can generally be achievedusing narrowband methods that are known in the art. Although system 20is shown and described as comprising multiple antennas at differentlocations on the patient's thorax, the ultra-wideband approach describedhere may alternatively be used advantageously in measurements of heartwall movement using only a single antenna.

The functions of I/Q cancellation unit 74 are also described in detailin PCT/IB2009/055438. Briefly, unit 74 modifies the phase and amplitudeof the sampled signals from RF digitizer 72, under the control of I/Qcontroller 76, so as to generate an anti-phased signal matching abackground component that is to be canceled. This background componentmay, for example, be a constant and/or slowly-varying part of theincoming signals, which is canceled in order to enhance the time-varyingsignal component that is due to heart motion. The I/Q cancellation unitgenerates a signal that is equal in amplitude to the backgroundcomponent but 180° out of phase and adds this anti-phased signal to thereceived signal from switching matrix 78 and digitizer 72. The I/Qcancellation unit thus cancels the background component withoutdegrading the actual radar signal from the body.

Processing circuitry 44 collects samples of the received signals,following background cancellation, and processes the samples to identifyand locate reflecting volumes within the thorax that correspond topoints on the heart surface. One method that may be used for thispurpose is the inverse spherical Radon transform. More specifically,PCT/IB2009/055438 describes a first-order approximation of the inversespherical Radon transform, which can be applied efficiently andeffectively to the sampled RF signals.

Alternatively, processing circuitry 44 may apply other transformtechniques. For example, the processing circuitry may compute afrequency response vector for each pair of antennas, and may then applya window function, such as a Kaiser window, to each vector and transformthe windowed frequency data to the time domain using an inverse FastFourier Transform (FFT). A time-domain filter, such as a Kalman filter,may be applied to the transformed data in order to model the locationand motion of the heart wall. The processing circuitry may correlatelocation and motion data between different antenna pairs, as well ascorrelating the motion with ECG measurements. Additionally oralternatively, circuitry 44 may perform ECG-gated or ECG-phasedbackground subtraction, wherein the subtracted background signal iscomputed as a combination of the different phases in the heartbeat.

In estimating the heart wall location, circuitry 44 may treat thereturned signal as a superposition of a number of point reflectors, eachmoving and scintillating at a predefined rate and in a predefinedmanner. The locations of the point reflectors are estimated usingoptimization techniques, such as a modified simplex technique. Theestimated locations are then used to calculate path length and amplitudeand thereby to calculate heart wall movement and/or liquid content ofthe lungs.

Further additionally or alternatively, processing circuitry 44 mayreceive and process other physiological parameters in conjunction withthe RF signals. For example, the processing circuitry may receivebreathing information, as well as data concerning patient posture,patient weight, and blood pressure.

Antenna Design

FIG. 4 is a schematic exploded view of a patch antenna unit 82, inaccordance with an embodiment of the present invention. The picturedantenna design may be used, for example, for any or all of the antennasshown in FIG. 1, as well as the antennas in the figures that follow.This design is suitable for production as a flexible patch, similar to alarge ECG electrode, which can be glued onto the body surface with asuitable adhesive. Antenna unit 82 is shown solely by way of example,however, and other types of antennas may similarly be used in system 20,as well as in the embodiments that are described below.

Antenna unit 82 comprises a front surface 84 in the form of a planarprinted circuit board (PCB), on which a conductive spiral 86 is printedto serve as the radiating element of the antenna, using methods ofprinted circuit fabrication that are known in the art. The front surfaceis made of suitable biocompatible materials in order to be brought intocontact with the body surface. (A layer of gel may be applied betweenfront surface 84 and the body surface, as explained above.) A rearelement 88 of the antenna, behind the front surface, serves as areflective structure. Element 88 comprises a ground plane 90 and aperiodic structure that create an electromagnetic band gap (EBG) betweenthe ground plane and the front surface. Details of the theory and designof this sort of antenna are provided by Bell et al., in “A Low-ProfileArchimedean Spiral Antenna Using an EBG Ground Plane,” IEEE Antennas andWireless Propagation Letters 3, pages 223-226 (2004), which isincorporated herein by reference.

The EBG structure in antenna unit 82 is made up of a periodic mesh ofconductive patches 92, which are connected to ground plane 90 by vias 94through a thin dielectric layer (omitted from the figure for visualclarity). The periodic mesh of rear element 88 can have Cartesian orcylindrical symmetry. Since different frequencies exhibit differentpower densities at different locations on the rear element surface, thecomponents of the EBG structure can have variable dimension to reflectthe different frequencies accordingly. For the frequency range mentionedabove (400 MHz to 4 GHz), the PCB making up front surface 84 may be 1.6mm thick, for example, while patches 92 are spaced 1.6 mm from groundplane 90 and contact the rear side of the front surface PCB whenassembled. The thickness of front surface 84 and the height of the EBG(as defined by vias 94) can be optimized for the target VSWRperformance, front lobe pattern and gain. Under these conditions, themesh of patches 92 creates an array of cavities having a parallelresonant response that mimics a perfect magnetic conductor in thespecified frequency range. The EBG structure thus reflects the backwardwave from spiral 86 in phase with the forward beam, therebyconstructively adding to the main forward beam from the antenna.

A flexible backing 96 covers the rear side of rear element 88. Backing96 extends over the edges of the front surface and rear element in orderto facilitate secure attachment of antenna unit 82 to the body surface.For this purpose, backing 96 may comprise an adhesive margin 98. Backing96 may comprise a conductive element for receiving ECG signals from thebody surface. Alternatively, front surface 84 may contain such aconductive element (not shown) alongside spiral 86, or the conductivespiral itself may serve to pick up the ECG signals. Additionally oralternatively, the antenna can be coated with metal and electrolytes toenable ECG measurement without affecting RF performance. A RF connector100 connects antenna unit 82 to cable 38. This connector conveys the RFexcitation signal to spiral 86 and returns both RF and ECG signals fromthe antenna unit to the cable.

Assessment of Pulmonary Edema

Referring back to FIG. 1, some of antennas 24, 26, 28, 30 and 32 arepositioned in such a way that the RF waves they emit and/or receive passthrough one of lungs 36. For example, when antenna 26 operates inmonostatic mode, it directs RF waves through the left lung toward heart24 and then receives reflected waves from the heart back through theleft lung. As another example, in bistatic mode, antenna 30 receives RFwaves emitted by antenna 24 after transmission through the lung. The RFpath length in either case will vary over the respiration cycle, as thelung fills with air and then empties, and it will vary depending on theamount of fluid accumulated in the lung. Processing circuitry 44 mayanalyze these path length variations in order to assess the amount offluid accumulation in the lung.

FIGS. 5A and 5B are schematic plots of propagation delay and amplitude,respectively, of RF waves reflected from the heart, in accordance withan embodiment of the present invention. These plots representmeasurements made on a healthy subject using an antenna configured andpositioned similarly to antenna 26. The scales are arbitrary. The delayand, to a lesser extent, the amplitude vary periodically with the heartcycle, as shown particularly by the sharp peaks in FIG. 5A.

The depressed portions of both plots between marks 260 and 290 on thehorizontal scale correspond to a period of inhalation during therespiratory cycle. This depression in FIG. 5A shows that when the lungsare full of air, the effective RF path length through the lungdecreases, since the physical distance between antenna 24 and heart 22remains about the same, while the average dielectric constant along thepath decreases. Exhalation empties the lungs of air and thus increasesthe effective RF path length. The amplitude of the reflected wave inFIG. 5B also drops during inhalation, presumably because of increasedvariations of the dielectric constant, and hence more reflections, alongthe RF path through the lung when the lung is filled with air.

For a lung with a high fluid content, the average dielectric constantwill typically be higher than a healthy lung, and the path delay of RFwaves traversing the lung will therefore be greater. The overallamplitude may also be greater due to reduced reflections as the wavestraverse the lungs. On the other hand, the difference between air-filledand empty lungs over the respiratory cycle is expected to be smaller inboth delay and amplitude than the differences shown in FIGS. 5A and 5B.Thus, to diagnose and monitor pulmonary edema, processing circuitry 44may, for example, compare the delay and possibly the amplitude of thereflected waves to benchmarks provided by healthy and edematous lungs,or to previous measurements made on the same patient. Additionally oralternatively, the processing circuitry may assess the amount of fluidin the lungs by analyzing the changes in delay and/or amplitude of thereflected waves over the course of one or more respiratory cycles.

In order to quantify the assessment of fluid accumulation, the actualphysical distance traversed by the RF waves passing through the lung maybe measured, and a relation (such as a ratio) may be computed betweenthe effective RF path length and the physical distance. For example,referring back to FIG. 1, if antennas 24 and 30 on opposite sides of thethorax are used to make a transmission-based measurement of the RF pathlength through lung 36, the physical distance between these antennas mayalso be measured. One way to measure the physical distance is bymechanical measurement, using a large caliper, for example.Alternatively or additionally, position sensors 48 attached to theantennas may be used to compute the spatial coordinates of each antenna,and the physical distance may then be computed simply as the Cartesiandistance between the coordinate points.

FIG. 6 is a schematic, pictorial illustration showing elements of asystem 110 for diagnosis of pulmonary edema, in accordance with anembodiment of the present invention. In this embodiment, antenna 26 isoperated monostatically to measure the effective path length of RF wavesthat are reflected from heart 22 via lung 36. An ultrasound transducer112 alongside antenna 26 is used to measure the physical distance to theheart and back. (Although antenna 26 and transducer 112 are shown, forthe sake of clarity, as separate units, they may alternatively beintegrated in a single package.) The heart wall is identified in boththe RF and ultrasound data as the nearest significantly movingreflective surface.

Processing circuitry 44 computes the relation between the physicaldistance traversed by the ultrasonic waves and the effective path lengthtraversed by the RF waves. Variations in this relation among differentpatients and among measurements at different points in time for a givenpatient are indicative of the amount of fluid in the lung.

Therapeutic Applications

Mechanical sensing of cardiac activity has been proposed for use incardiac stimulation therapy, such as optimizing timing intervals duringcardiac pacing. Detection of peak endocardial wall motion in the apex ofthe right ventricle for optimizing AV intervals has been validatedclinically. Systems and methods for using cardiac wall motion sensorsignals to provide hemodynamically-optimal values for heart rate and AVinterval have been described, for example, in U.S. Pat. No. 5,549,650,whose disclosure is incorporated herein by reference. A cardiacstimulating system designed to automatically optimize both the pacingmode and one or more pacing cycle parameters in a way that results inoptimization of a cardiac performance parameter, such as heartaccelerations, is generally described in U.S. Pat. No. 5,540,727, whosedisclosure is also incorporated herein by reference.

FIG. 7 is a schematic, pictorial illustration showing elements of asystem 120 for pacing heart 22 based on measurements of heart wallmotion, in accordance with an embodiment of the present invention. Forthe sake of simplicity, this figure shows a single antenna 26 used tomeasure motion of heart 22, but alternatively, multiple antennas may beused (as shown in FIG. 1, for example) to provide multi-dimensional wallmotion data. A pacing circuit 122 receives and processes the RF signalsfrom the antennas in order to measure the heart wall movement. Based onthis measurement, the pacing circuit generates pacing signals to drivepacing electrodes 124 in the heart. The pacing circuit may adjust thetiming and/or amplitude of the pacing signals adaptively, whilemeasuring the wall movement, in order to reach an optimal therapeuticresult.

As noted above, antenna 26 may also be used in assessing the fluidcontent of the lungs. The level of fluid content may then be used inadjusting the pacing regime of electrodes 124, as described, forexample, in U.S. Pat. No. 7,191,000, whose disclosure is incorporatedherein by reference.

Self-Contained Antenna Patch Unit

FIG. 8 is a block diagram that schematically illustrates a patch antennaunit 130, in accordance with another embodiment of the presentinvention. Patch 130, in effect, performs most of the functions ofsystem 20, using components that are contained inside an integratedpackage 142 having the form of a patch, which is typically no more than20×50 mm across (and may be smaller). As in the preceding embodiments,package 142 may include an adhesive layer (as shown in FIG. 4, forexample), by means of which unit 130 can be affixed to the patient'sskin.

Patch unit 130 comprises a flat antenna 132, which may be of one of thetypes described above. A transceiver 136 generates driving signals fortransmission by antenna 132 and filters and digitizes the reflectedsignals that the antenna receives from the patient's body. An activebackground cancellation circuit 134 cancels background components fromthe reflected signals, in a manner similar to that of I/Q cancellationunit 74, shown in FIG. 3. A processor 138 controls the operation of theother components of patch 130 and processes the digitized signals outputby transceiver 136 in order to extract heart wall motion data, in asimilar manner to processing circuitry 44. A power module 144, such as alow-profile battery, provides power to the components of the patch unit.

Patch unit 130 also comprises an ECG electrode 140, in electricalcontact with the patient's skin, and an ECG acquisition circuit 150,which filters and digitizes the ECG signals for input to processor 138.

Patch unit 130 may comprise a user interface, such as one or moreindicator LEDs 146, which signal the operational state of the patch(on/off, and possibly parameters such as battery level, quality of skincontact or signal strength). Alternatively or additionally, the userinterface may comprise a more informative display, such as a LCD, aswell as user controls, such as on/off and adjustment buttons.

A communication interface 148 communicates with a remote console (notshown), in order to transmit radar and ECG measurement data and possiblyto receive operational commands. The communication interface typicallycomprises a wireless link, such as a Bluetooth™ or WiFi link. Theconsole may be located in proximity to the patient's location and maythus receive data from interface 148 directly. Alternatively, interface148 may communicate with a local gateway, such as a personal computer orsmart phone, which communicates with the console over a network, such asthe Internet or a telephone network. In this sort of embodiment, forexample, the console may comprise a server, which stores the data forsubsequent viewing and analysis by a physician or other expert. Thissort of system configuration is particularly useful for extendedambulatory monitoring.

It will be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and subcombinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

1-59. (canceled)
 60. A diagnostic apparatus, comprising: one or more antennas each configured to be disposed on a thorax of a living body so as to direct radio frequency (RF) waves through a lung in the body and to output signals responsively to RF waves that have passed through the lung and reflected from the heart; and processing circuitry configured to process the signals over time to: determine at least one of an amplitude and a delay of the RF electromagnetic waves reflected from the heart, compare the at least one of the amplitude and the delay of the RF electromagnetic waves reflected from the heart to: benchmarks provided by healthy and edematous lungs, or previous measurements made on the same patient, and assess an amount of fluid in the lungs by analyzing the changes in delay and/or amplitude of the reflected RF waves over the course of one or more respiratory cycles.
 61. The apparatus of claim 60, further comprising a conductive element configured to receive electrocardiogram (ECG) signals from the outer surface of the body.
 62. The apparatus of claim 60, further comprising a communication interface for wirelessly communicating with a remote device.
 63. The apparatus of claim 60, further comprising a package which contains the antenna and processing the circuitry and is configured to be affixed as a patch to an outer surface of the body.
 64. The apparatus of claim 60, further comprising a coupling material having a predetermined dielectric constant.
 65. The apparatus of claim 60, wherein the coupling material is configured as one of a gel and an adhesive.
 66. The apparatus of claim 62, wherein the communication interface is configured to receive signals comprising commands from the remote device, the commands configured for operating the apparatus.
 67. The apparatus of claim 62, wherein the communication interface is configured to transmit the signals to the remote device via a gateway.
 68. The apparatus of claim 62, wherein the communication interface is configured to receive signals comprising commands from the remote device, the commands configured for operating the apparatus.
 69. The apparatus of claim 62, wherein the communication interface is configured to receive signals comprising commands from the remote device configured to store data received from the apparatus for at least one of subsequent viewing and analysis.
 70. The apparatus of claim 64, wherein the coupling material comprises an apparel.
 71. The apparatus of claim 70, wherein the apparel comprises a vest.
 72. The apparatus of claim 70, wherein the apparel is configured to accommodate at least one of the housing and the one or more antennas.
 73. A diagnostic apparatus, comprising: an antenna unit, which has a front surface configured to be brought into contact with an outer surface of a living body and which comprises: a planar antenna element, which is configured to direct radio frequency (RF) electromagnetic waves from the front surface into the body and to output RF signals responsively to the waves that are scattered from within the body; a conductive element, which is configured to receive electrocardiogram (ECG) signals from the outer surface of the body; and an adhesive patch configured for attachment to the outer surface of the living body; a cable, which is connected to the antenna unit so as to communicate with the planar antenna element and the conductive element; and processing circuitry, which is connected to the cable so as to receive and process the RF and ECG signals.
 74. The diagnostic apparatus of claim 73, wherein the processing circuitry is configured to determine at least one of an amplitude and a delay of the RF electromagnetic waves reflected from the heart.
 75. The diagnostic apparatus of claim 74, wherein the processing circuitry is configured to compare the at least one of the amplitude and the delay of the RF electromagnetic waves reflected from the heart to benchmarks provided by healthy and edematous lungs, or to previous measurements made on the same patient.
 76. The diagnostic apparatus of claim 74, wherein the processing circuitry is configured to assess an amount of fluid in the lungs by analyzing changes in delay and/or amplitude of the RF electromagnetic waves reflected from the heart over the course of one or more respiratory cycles.
 77. The apparatus of claim 73, further comprising a conductive element configured to receive electrocardiogram (ECG) signals from the outer surface of the body.
 78. The apparatus of claim 73, further comprising a communication interface for wirelessly communicating with a remote device.
 79. The apparatus of claim 73, further comprising a package which contains the antenna and processing the circuitry and is configured to be affixed as a patch to an outer surface of the body.
 80. The apparatus of claim 73, further comprising a coupling material having a predetermined dielectric constant.
 81. The apparatus of claim 73, wherein the coupling material is configured as one of a gel and an adhesive.
 82. The apparatus of claim 78, wherein the communication interface is configured to receive signals comprising commands from the remote device, the commands configured for operating the apparatus.
 83. The apparatus of claim 78, wherein the communication interface is configured to transmit the signals to the remote device via a gateway.
 84. The apparatus of claim 78, wherein the communication interface is configured to receive signals comprising commands from the remote device, the commands configured for operating the apparatus.
 85. The apparatus of claim 78, wherein the communication interface is configured to receive signals comprising commands from the remote device configured to store data received from the apparatus for at least one of subsequent viewing and analysis.
 86. The apparatus of claim 80, wherein the coupling material comprises an apparel.
 87. The apparatus of claim 86, wherein the apparel comprises a vest.
 88. The apparatus of claim 86, wherein the apparel is configured to accommodate at least one of the housing and the one or more antennas. 